The subject matter of the invention is a delay switch whereby electrical loads, such as electric lights controlled by a wall-mounted light switch, may be turned on either to remain on indefinitely, or alternatively to turn off after the elapse of a predetermined period of time as measured from the instant of switch actuation. Such devices in one form or another are long known in the art, and have proven themselves to be quite useful in automatically turning off such electrical loads as, for example, garage lights. In such situations the garage lights are turned on for a period of time while the operator is leaving the house to enter his car and drive off, the light automatically shutting down after a predetermined period of time. Alternatively, such timers find similar applications in lighting circuits, wherein the user actuates the timer to an automatic delayed power-off condition when he knows that he will be leaving the room with his arms encumbered, as a consequence of which he will be unable to turn the light switch off by hand.
A variety of timers are known in the art. Thus, for example, U.S. Pat. No. 4,002,925 issued to Monahan discloses a wall receptacle-mounted timer having a single toggle switch extending through a front mounting plate, the switch being actuatable to a variety of positions and providing not only delayed power-off, but also a delayed power-on feature as well. Because of the provision for a delayed power-on feature, the number of necessary switch positions is accordingly increased. The Monahan system suffers from the disadvantage that it cannot be inserted directly into the existing hot line wiring, but requires access to the low side of the line as well so as to provide power for an associated power supply used to power the timing circuitry, the supply being connected at all times across the power lines. Thus, to apply the Monahan system to existing wiring, an additional wire must be brought up to the conduit to the wall receptacle box. Morever, since the power supply in always on, there is a constant expenditure of power by the system, and as stated above, it is considered a desirable feature to eliminate all such parasitic power losses when the timing system is not operating in timing mode.
A related approach is disclosed in U.S. Pat. No. 4,336,464 issued to Weber, which discloses a timer insertable directly into the hot line without requiring access to the low (common) line, and which further shows a load-energized power supply deriving its current from the hot line without requiring connection to the low line. It therefore has the direct insertion feature previously described as desirable; however, no provision is made for turning off this power supply and the concomitant power consumption when the associated electrical load is driven in a conventional power-on condition, this power loss being present in both the power-on and timer-on modes of the system. Thus, an additional energy wastage is encountered. Additionally, the Weber system requires a pair of independent switches and does not show the desirable feature of a single actuating switch.
Thus, the prior art does not show in any one embodiment a simple time delay three-position wall mountable switch configured for direct replacement of conventional wall-mounted toggle switches and having associated timing circuitry which can be powered solely by access to the hot line to the load, and which draws no parasitic power whatever except when specifically actuated to the timing mode. Such a device would constitute a new, useful, and non-obvious contribution to the art.